Memory cell and method of operating the same

ABSTRACT

A memory cell includes a write bit line, a write transistor and a read transistor. The write transistor is coupled between the write bit line and a first node. The read transistor is coupled to the write transistor by the first node. The read transistor includes a ferroelectric layer. The write transistor is configured to set a stored data value of the memory cell by a write bit line signal that adjusts a polarization state of the read transistor. The polarization state corresponds to the stored data value.

PRIORITY CLAIM

This application claims the benefit of U.S. Provisional Application No.63/031,851, filed May 29, 2020, which is herein incorporated byreference in its entirety.

BACKGROUND

The semiconductor integrated circuit (IC) industry has produced a widevariety of digital devices to address issues in a number of differentareas. Some of these digital devices, such as memory macros, areconfigured for the storage of data. As ICs have become smaller and morecomplex, the resistance of conductive lines within these digital devicesare also changed affecting the operating voltages of these digitaldevices and overall IC performance.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a block diagram of a memory cell array, in accordance withsome embodiments.

FIG. 2A is a circuit diagram of a memory cell, in accordance with someembodiments.

FIG. 2B is a circuit diagram of a memory cell, in accordance with someembodiments.

FIG. 2C is a circuit diagram of a memory cell, in accordance with someembodiments.

FIG. 3A is a circuit diagram of a memory cell, in accordance with someembodiments.

FIG. 3B is a circuit diagram of a memory cell, in accordance with someembodiments.

FIG. 3C is a circuit diagram of a memory cell, in accordance with someembodiments.

FIG. 4A is a circuit diagram of a memory cell, in accordance with someembodiments.

FIG. 4B is a circuit diagram of a memory cell, in accordance with someembodiments.

FIG. 4C is a circuit diagram of a memory cell, in accordance with someembodiments.

FIG. 5 is a cross-sectional view of an integrated circuit, in accordancewith some embodiments.

FIG. 6 is a functional flow chart of a method of manufacturing anintegrated circuit, in accordance with some embodiments.

FIG. 7 is a flowchart of a method of operating a circuit, in accordancewith some embodiments.

DETAILED DESCRIPTION

The following disclosure provides different embodiments, or examples,for implementing features of the provided subject matter. Specificexamples of components, materials, values, steps, arrangements, or thelike, are described below to simplify the present disclosure. These are,of course, merely examples and are not limiting. Other components,materials, values, steps, arrangements, or the like, are contemplated.For example, the formation of a first feature over or on a secondfeature in the description that follows may include embodiments in whichthe first and second features are formed in direct contact, and may alsoinclude embodiments in which additional features may be formed betweenthe first and second features, such that the first and second featuresmay not be in direct contact. In addition, the present disclosure mayrepeat reference numerals and/or letters in the various examples. Thisrepetition is for the purpose of simplicity and clarity and does not initself dictate a relationship between the various embodiments and/orconfigurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

In accordance with some embodiments, a memory cell includes a write bitline, a write transistor and a read transistor. The write transistor iscoupled between the write bit line and a first node. The read transistoris coupled to the write transistor by the first node. The writetransistor is configured to set a stored data value of the memory cellby a write bit line signal that adjusts a polarization state of the readtransistor. In some embodiments, the polarization state corresponds tothe stored data value of the memory cell.

In some embodiments, the read transistor includes a first gate terminalcoupled to the write transistor by the first node, and a ferroelectricregion having the polarization state that corresponds to the stored datavalue of the memory cell.

In some embodiments, by using the ferroelectric region in the memorycell, the memory cell has less charge leakage at the first node comparedto other approaches. In some embodiments, by using the ferroelectricregion in the memory cell, the ferroelectric region is able to hold ormaintain the polarization state even after voltage at the first node isremoved thereby resulting in the memory cell having a longer dataretention time and a larger memory window than other approaches. In someembodiments, by having at least a longer data retention time or a largermemory window than other approaches, the memory cell is refreshed lessthan other approaches resulting in less power consumption than otherapproaches.

FIG. 1 is a block diagram of a memory cell array 100, in accordance withsome embodiments. In some embodiments, memory cell array 100 is part ofan integrated circuit.

Memory cell array 100 comprises an array of memory cells 102[1,1],102[1,2], . . . , 102[2,2], . . . , 102[M,N] (collectively referred toas “array of memory cells 102A”) having M rows and N columns, where N isa positive integer corresponding to the number of columns in array ofmemory cells 102A and M is a positive integer corresponding to thenumber of rows in array of memory cells 102A. The rows of cells in arrayof memory cells 102A are arranged in a first direction X. The columns ofcells in array of memory cells 102A are arranged in a second directionY. The second direction Y is different from the first direction X. Insome embodiments, the second direction Y is perpendicular to the firstdirection X. Each memory cell 102[1,1], 102[1,2], . . . , 102[2,2], . .. , 102[M,N] in array of memory cells 102A is configured to store acorresponding bit of data.

Array of memory cells 102A is a dynamic random-access memory (DRAM)array including DRAM-like memory cells. In some embodiments, each memorycell in array of memory cells 102A corresponds to a two transistor (2T)memory cell with 1-Ferroelectric field effect transistor (FeFET) asshown in FIGS. 2A-2C. In some embodiments, each memory cell in array ofmemory cells 102A corresponds to a three transistor (3T) memory cellwith 1-FeFET as shown in FIGS. 3A-3C. In some embodiments, each memorycell in array of memory cells 102A corresponds to a four transistor (4T)memory cell with 1-FeFET as shown in FIGS. 4A-4C.

Different types of memory cells in array of memory cells 102A are withinthe contemplated scope of the present disclosure. For example, in someembodiments, each memory cell in array of memory cells 102A is a staticrandom access memory (SRAM). In some embodiments, each memory cell inarray of memory cells 102A corresponds to a ferroelectric resistiverandom-access memory (FeRAM) cell. In some embodiments, each memory cellin array of memory cells 102A corresponds to a magneto-resistiverandom-access memory (MRAM) cell. In some embodiments, each memory cellin array of memory cells 102A corresponds to a resistive random-accessmemory (RRAM) cell. Other configurations of array of memory cells 102Aare within the scope of the present disclosure.

Memory cell array 100 further includes M write word lines WWL[1], . . .WWL[M] (collectively referred to as “write word line WWL”). Each row 1,. . . , M in array of memory cells 102A is associated with acorresponding write word line WWL[1], . . . , WWL[M]. Each row of memorycells in array of memory cells 102A is coupled with a correspondingwrite word line WWL[1], . . . , WWL[M]. For example, memory cells102[1,1], 102[1,2], . . . , 102[1,N] in row 1 are coupled with writeword line WWL[1]. Each write word line WWL extends in the firstdirection X.

Memory cell array 100 further includes M read word lines RWL[1], . . .RWL[M] (collectively referred to as “read word line RWL”). Each row 1, .. . , M in array of memory cells 102A is associated with a correspondingread word line RWL[1], . . . , RWL[M]. Each row of memory cells in arrayof memory cells 102A is coupled with a corresponding read word lineRWL[1], . . . , RWL[M]. For example, memory cells 102[1,1], 102[1,2], .. . , 102[1,N] in row 1 are coupled with read word line RWL[1]. Eachread word line RWL extends in the first direction X.

Memory cell array 100 further includes N write bit lines WBL[1], . . .WBL[N] (collectively referred to as “write bit line WBL”). Each column1, . . . , N in array of memory cells 102A is associated with acorresponding write bit line WBL[1], . . . , WBL[N]. Each column ofmemory cells in array of memory cells 102A is coupled with acorresponding write bit line WBL[1], . . . , WBL[N]. For example, memorycells 102[1,1], 102[2,1], . . . , 102[M,1] in column 1 are coupled withwrite bit line WBL[1]. Each write bit line WBL extends in the seconddirection Y.

Memory cell array 100 further includes N read bit lines RBL[1], . . .RBL[N] (collectively referred to as “read bit line RBL”). Each column 1,. . . , N in array of memory cells 102A is associated with acorresponding read bit line RBL[1], . . . , RBL[N]. Each column ofmemory cells in array of memory cells 102A is coupled with acorresponding read bit line RBL[1], . . . , RBL[N]. For example, memorycells 102[1,1], 102[2,1], . . . , 102[M,1] in column 1 are coupled withread bit line RBL[1]. Each read bit line RBL extends in the seconddirection Y.

Other configurations of memory cell array 100 are within the scope ofthe present disclosure. Different configurations of at least write bitlines BL, write word lines WWL, read bit lines RBL or read word linesRWL in memory cell array 100 are within the contemplated scope of thepresent disclosure. In some embodiments, memory cell array 100 includesadditional write ports (write word lines WWL or write bit lines WBL)and/or read ports (read word lines RWL or read bit lines RBL).Furthermore, in some embodiments, array of memory cells 102A includesmultiple groups of different types of memory cells.

By way of an illustrative example, a write operation is performed tomemory cell 102[1,1] located in row 1 and column 1 of array of memorycells 102A. Row 1 includes memory cells 102[1,1], 102[1,2], . . . ,102[1,N] that are selected by write word line WWL[1]. Column 1 includesmemory cells 102[1,1], 102[2,1], . . . , 102[M,1] that are selected forreceiving a data signal and storing a binary bit of data by write bitline WBL[1]. Together, write word line WWL[1] and write bit line WBL[1]select and store a binary bit of data in memory cell 102[1,1].

By way of an illustrative example, a read operation is performed tomemory cell 102[1,1] located in row 1 and column 1 of array of memorycells 102A. Row 1 includes memory cells 102[1,1], 102[1,2], . . . ,102[1,N] that are selected by read word line RWL[1]. Column 1 includesmemory cells 102[1,1], 102[2,1], . . . , 102[M,1] that are selected toaccess the stored binary bit of data by read bit line RBL[1]. Together,read word line RWL[1] and read bit line RBL[1] select and read thebinary bit of data stored in memory cell 102[1,1].

FIG. 2A is a circuit diagram of a memory cell 200A, in accordance withsome embodiments.

Memory cell 200A is an embodiment of a memory cell in array of memorycells 102A of FIG. 1 expressed in a schematic diagram, and similardetailed description is therefore omitted.

Components that are the same or similar to those in one or more of FIGS.2A-2C, 3A-3C, 4A-4C (shown below) are given the same reference numbers,and detailed description thereof is thus omitted. For ease ofillustration, some of the labeled elements of FIGS. 2A-2C, 3A-3C, 4A-4Care not labelled in each of FIGS. 2A-2C, 3A-3C, 4A-4C. In someembodiments, FIGS. 2A-2C, 3A-3C, 4A-4C include additional elements notshown in FIGS. 2A-2C, 3A-3C, 4A-4C.

Memory cell 200A is usable as one or more memory cells in array ofmemory cells 102A of FIG. 1 .

Memory cell 200A includes a write transistor M1, a read transistor M2, awrite word line WWL, a read word line RWL, a write bit line WBL and aread bit line RBL.

Write word line WWL corresponds to a write word line of write word linesWWL[1], . . . , WWL[M], read word line RWL corresponds to a read wordline of read word lines RWL[1], . . . , RWL[M], write bit line WBLcorresponds to a write bit line of write bit lines WBL[1], . . . ,WBL[N], and read bit line RBL corresponds to a read bit line of read bitlines RBL[1], . . . , RBL[N] of FIG. 1 , and similar detaileddescription is therefore omitted.

Write transistor M1 includes a gate terminal coupled to write word lineWWL, a drain terminal coupled to write bit line WBL, and a sourceterminal coupled to at least a gate terminal of read transistor M2 by anode ND1. Write transistor M1 is configured to write data in memory cell200A. Write transistor M1 is enabled (e.g., turned on) or disabled(e.g., turned off) in response to a write bit line signal on the writebit line WBL.

Write transistor M1 is shown as a P-type Metal Oxide Semiconductor(PMOS) transistor. In some embodiments, write transistor M1 is an N-typeMetal Oxide Semiconductor (NMOS) transistor.

Read transistor M2 includes a drain terminal coupled to read word lineRWL, a source terminal coupled to read bit line RBL, and a gate terminalcoupled to the source terminal of write transistor M1.

Read transistor M2 is referred to as a ferroelectric field effecttransistor (FeFET) device, as read transistor M2 includes aferroelectric region 202 positioned within the gate terminal of the readtransistor M2. The ferroelectric region 202 is configured to havedifferent polarization states based on the voltage applied to the gateof the read transistor M2. The polarization of the ferroelectric region202 determines the conductivity (e.g., low resistance state or highresistance state) of read transistor M2 which represents the data storedin read transistor M2.

Data is stored by programming the ferroelectric region 202 to havedifferent polarization states. The different polarization states createtwo different threshold voltage states (e.g., Vth) that correspond to alogic ‘1’ and a logic ‘0’. Due to the threshold voltage difference, theferroelectric region 202 in the read transistor M2 is configured to usespecific gate voltages based on its logic state to turn on. In someembodiments, the difference between these gate voltages is referred toas memory window.

The binary states of stored data in memory cell 200A are encoded in theform of the polarization of the ferroelectric region 202. The directionor value of the polarization (e.g., +P or −P) of the ferroelectricregion 202 determines the resistance state (e.g., low or high) of theread transistor M2. In some embodiments, a low resistance state of theread transistor M2 corresponds to the read transistor M2 being turned onor conducting, and a high resistance state of the read transistor M2corresponds to the read transistor M2 being turned off or notconducting. In some embodiments, a low resistance state of the readtransistor M2 corresponds to a first stored value (e.g., logic “0” or“1”), and a high resistance state of the read transistor M2 correspondsto a second stored value (e.g., logic “1” or “0”) opposite from thefirst stored value. A voltage of the gate of the read transistor M2 ornode ND1 controls the polarization states and corresponding electricfield in the ferroelectric region 202 of read transistor M2.

Write transistor M1 is configured to write data by controlling thevoltage of node ND1 or the gate of read transistor M2 therebycontrolling the polarization states of the ferroelectric region 202 ofread transistor M2. In some embodiments, if the write transistor M1 isenabled or turned on, a voltage of the write bit line WBL is configuredto control the voltage of the node ND1 or the gate of read transistorM2. Thus, in some embodiments, the polarized state of the ferroelectricregion 202 is controlled by the voltage of the write bit line WBL. Insome embodiments, the voltage of the write bit line WBL corresponds tothe data stored in memory cell 200A. In some embodiments, thepolarization state of the ferroelectric region 202 is maintained evenafter an electric field or a corresponding voltage at node ND1 isremoved, and the read transistor M2 is a non-volatile transistor device.

Read transistor M2 is configured to read data stored in memory cell200A. In some embodiments, read transistor M2 is configured to outputdata stored in memory cell 200A based on whether read transistor M2 isturned on or off. The polarization state of the ferroelectric region 202determines whether read transistor M2 is turned on or off.

In some embodiments, write transistor M1 and read transistor M2 eachinclude channel regions that are formed of a same type of material. Insome embodiments, write transistor M1 and read transistor M2 each havechannel regions that have a silicon body or bulk.

Read transistor M2 is shown as a PMOS transistor. In some embodiments,read transistor M2 is an NMOS transistor.

During a write operation of memory cell 200A, the voltage of the writebit line WBL (e.g., data to be stored in memory cell 200A) is set by awrite driver circuit (not shown), and the write word line WWL is set toa logical low thereby turning on write transistor M1. In response towrite transistor M1 being turned on, the voltage of the write bit lineWBL is applied to the gate of read transistor M2 or node ND1. As thevoltage of the write bit line WBL is applied to the gate of readtransistor M2 or node ND1, the write bit line voltage controls thepolarization state of the ferroelectric region 202 and the correspondingdata stored by read transistor M2. In other words, the voltage of thewrite bit line WBL is used to set the read transistor M2 in a lowresistance state (e.g., conducting) or a high resistance state (e.g.,not conducting). Afterwards, the write word line WWL is set to a logicalhigh thereby turning off write transistor M1.

In response to write transistor M1 being turned off, data stored inmemory cell 200A is held, and memory cell 200A is in a hold mode.

By using ferroelectric region 202 in memory cell 200A, memory cell 200Adoes not have charge leakage at node ND1 compared to other approaches(such as DRAM). By using ferroelectric region 202 in memory cell 200A,the non-volatile nature of the ferroelectric material in ferroelectricregion 202 is able to hold or maintain the polarization state even afterthe voltage at node ND1 is removed thereby resulting in a longer dataretention time and a larger memory window than other approaches. Byhaving at least a longer data retention time or a larger memory windowthan other approaches, memory cell 200A is refreshed less than otherapproaches resulting in less power consumption than other approaches.

In some embodiments, memory cell 200A and memory cells 200B-200C (FIGS.2B-2C) have a 2T memory cell structure that is compatible withcomplementary metal oxide semiconductor (CMOS) processes and istherefore scalable.

During a read operation of memory cell 200A, the voltage of the read bitline RBL is pre-discharged to a logical low, and the read word line RWLis raised to a logical high. In some embodiments, if the read transistorM2 is in a low resistance state, then the read transistor M2 is turnedon or conducting, and the current from the read word line RWL throughthe read transistor M2 to the read bit line RBL is sensed by a senseamplifier (not shown), and the data associated with the read transistorM2 being in a low resistance state (e.g., “1” or “0”) is read out. Insome embodiments, if the read transistor M2 is in a high resistancestate, then the read transistor M2 is turned off or not conducting, andthe current from the read word line RWL through the read transistor M2to the read bit line RBL is sensed by a sense amplifier (not shown), andthe data associated with the read transistor M2 being in a highresistance state (e.g., “0” or “1”) is read out. In this embodiment, thecurrent through the read transistor M2 is negligible since the readtransistor M2 is turned off. Afterwards, the read word line RWL is setto a logical low.

Other transistor terminals for each of the transistors M1, M2, M1′ orM2′ (described below) of the present application are within the scope ofthe present disclosure. For example, reference to the drains and sourcesof a same transistor in the present disclosure can be changed to asource and a drain of the same transistor. Thus, for write transistorM1, reference to the drain and source of write transistor M1 can bechanged to the source and drain of write transistor M1, respectively.Similarly, for read transistor M2, reference to the drain and source ofread transistor M2 can be changed to the source and drain of readtransistor M2, respectively.

Other configurations or quantities of transistors in memory cell 200Aare within the scope of the present disclosure.

FIG. 2B is a circuit diagram of a memory cell 200B, in accordance withsome embodiments.

Memory cell 200B is an embodiment of a memory cell in array of memorycells 102A of FIG. 1 expressed in a schematic diagram, and similardetailed description is therefore omitted.

Memory cell 200B is usable as one or more memory cells in array ofmemory cells 102A of FIG. 1 . Memory cell 200B includes a writetransistor M1′, read transistor M2, write word line WWL, read word lineRWL, write bit line WBL and read bit line RBL.

Memory cell 200B is a variation of memory cell 200A of FIG. 2A, andsimilar detailed description is therefore omitted. In comparison withmemory cell 200A of FIG. 2A, write transistor M1′ replaces writetransistor M1 of FIG. 2A, and similar detailed description is thereforeomitted.

Write transistor M1′ is shown as a PMOS transistor. In some embodiments,write transistor M1′ is an NMOS transistor. In some embodiments, writetransistor M1′ is similar to write transistor M1 of FIG. 2A, and similardetailed description is therefore omitted. The operation of memory cell200B is similar to the operation of memory cell 200A described above,and similar detailed description is therefore omitted.

In comparison with write transistor M1 of FIG. 2A, write transistor M1′includes an oxide channel region 210, and similar detailed descriptionis therefore omitted. In some embodiments, one or more transistorshaving oxide channel regions of the present disclosure include thin filmtransistors (TFTs). In some embodiments, the oxide channel region 210for write transistor M1′ includes an oxide semiconductor materialincluding zinc oxide, cadmium oxide, indium oxide, IGZO, SnO₂, TiO₂, orcombinations thereof, or the like. Other transistor types or oxidematerials for write transistor M1′ are within the scope of the presentdisclosure.

In some embodiments, by including write transistor M1′ with an oxidechannel region 210 and an FeFET read transistor M2, memory cell 200B haslower leakage current than other approaches that do not include an oxidechannel region in the write transistor. In some embodiments, by reducingthe leakage current of memory cell 200B, memory cell 200B has a longerdata retention time than other approaches. By having a longer dataretention time than other approaches, memory cell 200B is refreshed lessthan other approaches resulting in less power consumption than otherapproaches. In some embodiments, by reducing the leakage current ofmemory cell 200B, memory cell 200B has less write disturbance errorsthan other approaches. Furthermore, since memory cell 200B is similar tomemory cell 200A, memory cell 200B also has the benefits discussed abovewith respect to memory cell 200A. In some embodiments, the oxide channelregion 210, 220, 230 or 240 of memory cell 200B-200C, 300B-300C and400B-400C (FIGS. 2B-2C, 3B-3C & 4B-4C) can be integrated into a back endof line (BEOL) process thereby increasing the memory density of memorycell 200B-200C, 300B-300C and 400B-400C.

Other configurations, connections or quantities of transistors in memorycell 200B are within the scope of the present disclosure.

FIG. 2C is a circuit diagram of a memory cell 200C, in accordance withsome embodiments.

Memory cell 200C is an embodiment of a memory cell in array of memorycells 102A of FIG. 1 expressed in a schematic diagram, and similardetailed description is therefore omitted.

Memory cell 200C is usable as one or more memory cells in array ofmemory cells 102A of FIG. 1 . Memory cell 200C includes write transistorM1′, a read transistor M2′, write word line WWL, read word line RWL,write bit line WBL and read bit line RBL.

Memory cell 200C is a variation of memory cell 200B of FIG. 2B, andsimilar detailed description is therefore omitted. In comparison withmemory cell 200B of FIG. 2B, read transistor M2′ replaces readtransistor M2 of FIG. 2B, and similar detailed description is thereforeomitted.

Read transistor M2′ is shown as a PMOS transistor. In some embodiments,read transistor M2′ is an NMOS transistor. In some embodiments, readtransistor M2′ is similar to read transistor M2 of FIGS. 2A-2B, andsimilar detailed description is therefore omitted. The operation ofmemory cell 200C is similar to the operation of memory cell 200A(described above) or memory cell 200B, and similar detailed descriptionis therefore omitted.

In comparison with read transistor M2 of FIG. 2B, read transistor M2′includes an oxide channel region 220, and similar detailed descriptionis therefore omitted. In some embodiments, the oxide channel region 220for read transistor M2′ includes an oxide semiconductor materialincluding zinc oxide, cadmium oxide, indium oxide, IGZO, SnO₂, TiO₂, orcombinations thereof, or the like.

In some embodiments, the oxide channel region 220 of read transistor M2′includes the same oxide semiconductor material as the oxide channelregion 210 of write transistor M1′. In some embodiments, the oxidechannel region 220 of read transistor M2′ includes a different oxidesemiconductor material as the oxide channel region 210 of writetransistor M1′. Other transistor types or oxide materials for readtransistor M2′ are within the scope of the present disclosure.

In some embodiments, read transistor M2′ includes an oxide channelregion 220, and write transistor M1′ includes a silicon channel regionhaving a silicon body or bulk similar to write transistor M1.

In some embodiments, by including write transistor M1′ with an oxidechannel region 210 and read transistor M2′ with an oxide channel region220 and as an FeFET, memory cell 200C has lower leakage current thanother read transistor approaches. In some embodiments, by reducing theleakage current of memory cell 200C, memory cell 200C has the benefitsdiscussed above with respect to memory cell 200B. Furthermore, sincememory cell 200C is similar to memory cell 200A, memory cell 200C alsohas the benefits discussed above with respect to memory cell 200A.

Other configurations, connections or quantities of transistors in memorycell 200C are within the scope of the present disclosure.

FIG. 3A is a circuit diagram of a memory cell 300A, in accordance withsome embodiments.

Memory cell 300A is an embodiment of a memory cell in array of memorycells 102A of FIG. 1 expressed in a schematic diagram, and similardetailed description is therefore omitted.

Memory cell 300A is usable as one or more memory cells in array ofmemory cells 102A of FIG. 1 . Memory cell 300A includes write transistorM1, read transistor M2, write word line WWL, read word line RWL, writebit line WBL, read bit line RBL and a transistor M3.

Memory cell 300A is a variation of memory cell 200A of FIG. 2A, andsimilar detailed description is therefore omitted. In comparison withmemory cell 200A of FIG. 2A, memory cell 300A further includestransistor M3, and similar detailed description is therefore omitted.

Transistor M3 includes a source terminal coupled to read bit line RBL, adrain terminal coupled to the source terminal of read transistor M2, anda gate terminal configured to receive a control signal CS. In someembodiments, transistor M3 is turned on or turned off in response tocontrol signal CS. For example, in some embodiments, during a readoperation of a selected memory cell, similar to memory cell 300A, theselected memory cell includes a selected transistor M3, and unselectedmemory cells, similar to memory cell 300A, include an unselectedtransistor M3. In these embodiments, selected transistor M3 is turned onin response to a first value of control signal CS, and unselectedtransistors M3 in corresponding unselected cells are turned off inresponse to a second value of control signal CS. In these embodiments,the second value of control signal CS is inverted from the first valueof control signal CS. In these embodiments, the transistors M3 inunselected memory cells are turned off thereby reducing leakage current.

In comparison with memory cell 200A of FIG. 2A, the source terminal ofread transistor M2 of FIGS. 3A-3C is coupled with the drain terminal oftransistor M3, and is therefore not directly coupled with the read bitline RBL as is shown in FIG. 2A.

Transistor M3 of FIGS. 3A-3B is enabled or disabled in response to acontrol signal CS. Transistor M3 is configured to electricallycouple/decouple read transistor M2 to/from the read bit line RBL inresponse to control signal CS. For example, if control signal CS islogically low, transistor M3 is enabled or turned on, and transistor M3thereby electrically couples the source of read transistor M2 to theread bit line RBL. For example, if control signal CS is logically high,transistor M3 is disabled or turned off, and transistor M3 therebyelectrically decouples the source of read transistor M2 from the readbit line RBL.

The operation of memory cell 300A is similar to the operation of memorycell 200A described above, and similar detailed description is thereforeomitted. For example, in comparison with the write operation of memorycell 200A of FIG. 2A, during the write operation of memory cell 300A,transistor M3 is disabled or turned off, and the operation of the otherportions of memory cell 300A are similar to the write operation ofmemory cell 200A described above, and similar detailed description istherefore omitted. For example, in comparison with the read operation ofmemory cell 200A of FIG. 2A, during the read operation of memory cell300A, transistor M3 is enabled or turned on, and the operation of theother portions of memory cell 300A are similar to the read operation ofmemory cell 200A described above, and similar detailed description istherefore omitted.

Transistor M3 is shown as a PMOS transistor. In some embodiments,transistor M3 is an NMOS transistor.

In some embodiments, transistor M3 and at least write transistor M1 orread transistor M2, include channel regions that are formed of a sametype of material. In some embodiments, transistor M3 has a channelregion that has a silicon body or bulk. In some embodiments, transistorM3 and at least write transistor M1 or read transistor M2, includechannel regions that have a silicon body or bulk.

In some embodiments, by including write transistor M1, read transistorM2 (e.g., FeFET), and transistor M3, memory cell 300A is similar tomemory cell 200A. In some embodiments, since memory cell 300A is similarto memory cell 200A, memory cell 300A has the benefits discussed abovewith respect to memory cell 200A.

In some embodiments, memory cell 300A and memory cells 300B-300C (FIGS.3B-3C) have a 3T memory cell structure that is compatible with CMOSprocesses and is therefore scalable.

Other transistor terminals for each of transistors M1, M2, M3, M1′, M2′and M3′ of the present application are within the scope of the presentdisclosure. For example, reference to the drains and sources of a sametransistor in the present disclosure can be changed to a source and adrain of the same transistor.

Other configurations or quantities of transistors in memory cell 300Aare within the scope of the present disclosure.

FIG. 3B is a circuit diagram of a memory cell 300B, in accordance withsome embodiments.

Memory cell 300B is an embodiment of a memory cell in array of memorycells 102A of FIG. 1 expressed in a schematic diagram, and similardetailed description is therefore omitted.

Memory cell 300B is usable as one or more memory cells in array ofmemory cells 102A of FIG. 1 . Memory cell 300B includes write transistorM1′, read transistor M2, write word line WWL, read word line RWL, writebit line WBL, read bit line RBL and transistor M3.

Memory cell 300B is a variation of memory cell 300A of FIG. 3A andmemory cell 200B of FIG. 2B, and similar detailed description istherefore omitted. For example, memory cell 300B combines featuressimilar to memory cell 300A of FIG. 3A and memory cell 200B of FIG. 2B.

In comparison with memory cell 300A of FIG. 3A, write transistor M1′ ofFIG. 2B replaces write transistor M1 of FIG. 3A, and similar detaileddescription is therefore omitted.

Write transistor M1′ is described in memory cell 200B of FIG. 2B, andsimilar detailed description is therefore omitted. Write transistor M1′is shown as a PMOS transistor. In some embodiments, write transistor M1′is an NMOS transistor. The operation of memory cell 300B is similar tothe operation of memory cell 300A described above, and similar detaileddescription is therefore omitted.

In some embodiments, by including write transistor M1′ with an oxidechannel region 210, read transistor M2 (e.g., FeFET) and transistor M3,memory cell 300B achieves benefits similar to the benefits discussedabove with respect to memory cell 300A and memory cell 200B.

Furthermore, since memory cell 300B is similar to memory cell 200A,memory cell 300B also has the benefits discussed above with respect tomemory cell 200A.

Other configurations, connections or quantities of transistors in memorycell 300B are within the scope of the present disclosure.

FIG. 3C is a circuit diagram of a memory cell 300C, in accordance withsome embodiments.

Memory cell 300C is an embodiment of a memory cell in array of memorycells 102A of FIG. 1 expressed in a schematic diagram, and similardetailed description is therefore omitted.

Memory cell 300C is usable as one or more memory cells in array ofmemory cells 102A of FIG. 1 . Memory cell 300C includes write transistorM1′, read transistor M2′, write word line WWL, read word line RWL, writebit line WBL, read bit line RBL and a transistor M3′.

Memory cell 300C is a variation of memory cell 300B of FIG. 3B, andsimilar detailed description is therefore omitted. In comparison withmemory cell 300B of FIG. 3B, read transistor M2′ replaces readtransistor M2 of FIG. 3B and transistor M3′ replaces transistor M3 ofFIG. 3B, and similar detailed description is therefore omitted.

Read transistor M2′ is described in memory cell 200C of FIG. 2C, andsimilar detailed description is therefore omitted. Read transistor M2′is shown as a PMOS transistor. In some embodiments, read transistor M2′is an NMOS transistor.

Transistor M3′ is shown as a PMOS transistor. In some embodiments,transistor M3′ is an NMOS transistor. In some embodiments, transistorM3′ is similar to transistor M3 of FIGS. 3A-3B, and similar detaileddescription is therefore omitted. The operation of memory cell 300C issimilar to the operation of memory cell 300A (described above) or memorycell 300B, and similar detailed description is therefore omitted.

In comparison with transistor M3 of FIG. 3B, transistor M3′ includes anoxide channel region 230, and similar detailed description is thereforeomitted. In some embodiments, the oxide channel region 230 fortransistor M3′ includes an oxide semiconductor material including zincoxide, cadmium oxide, indium oxide, IGZO, SnO₂, TiO₂, or combinationsthereof, or the like.

In some embodiments, the oxide channel region 230 of transistor M3′includes the same oxide semiconductor material as the oxide channelregion 210, 220 of at least write transistor M1′ or read transistor M2′.In some embodiments, the oxide channel region 230 of transistor M3′includes a different oxide semiconductor material as the oxide channelregion 210, 220 of at least write transistor M1′ or read transistor M2′.Other transistor types or oxide materials for transistor M3′ are withinthe scope of the present disclosure.

In some embodiments, one of read transistor M2′ or transistor M3′includes an oxide channel region 220 or 230, and the other of readtransistor M2′ or transistor M3′ includes a silicon channel regionhaving a silicon body or bulk similar to read transistor M2 ortransistor M3, respectively.

In some embodiments, by including write transistor M1′ with an oxidechannel region 210, read transistor M2′ with an oxide channel region 220and as an FeFET, and transistor M3′ with an oxide channel region 230,memory cell 300C achieves benefits similar to the benefits discussedabove with respect to memory cell 300A and memory cell 200C.Furthermore, since memory cell 300C is similar to memory cell 200A,memory cell 300C also has the benefits discussed above with respect tomemory cell 200A.

Other configurations, connections or quantities of transistors in memorycell 300C are within the scope of the present disclosure.

FIG. 4A is a circuit diagram of a memory cell 400A, in accordance withsome embodiments.

Memory cell 400A is an embodiment of a memory cell in array of memorycells 102A of FIG. 1 expressed in a schematic diagram, and similardetailed description is therefore omitted.

Memory cell 400A is usable as one or more memory cells in array ofmemory cells 102A of FIG. 1 . Memory cell 400A includes write transistorM1, read transistor M2, write word line WWL, read word line RWL, writebit line WBL, read bit line RBL, transistor M3 and a transistor M4.

Memory cell 400A is a variation of memory cell 300A of FIG. 3A, andsimilar detailed description is therefore omitted. In comparison withmemory cell 300A of FIG. 3A, memory cell 400A further includestransistor M4, and similar detailed description is therefore omitted.

Transistor M4 includes a drain terminal, a gate terminal and a sourceterminal. The drain terminal of transistor M4 is coupled to read writeline RWL. The gate terminal of transistor M4 is coupled to the drainterminal of write transistor M1, the gate terminal of read transistor M2and node ND1. The source terminal of transistor M4 is coupled to a nodeND2. In some embodiments, node ND2 is electrically coupled to areference voltage supply. In some embodiments, the reference voltagesupply has a reference voltage VSS. In some embodiments, the referencevoltage supply corresponds to ground.

Transistor M4 of FIGS. 4A-4C is enabled or disabled in response to avoltage of node ND1. In some embodiments, the voltage of node ND1corresponds to the write bit line signal, and thus transistor M4 ofFIGS. 4A-4C is enabled or disabled in response to the write bit linesignal.

Transistor M4 of FIGS. 4A-4C is configured to electricallycouple/decouple the read word line RWL to/from node ND2 in response tothe write bit line signal on the write bit line WBL. For example, if thewrite bit line signal is logically low, transistor M4 is enabled orturned on, and transistor M4 thereby electrically couples the read wordline RWL to node ND2. For example, if the write bit line signal islogically high, transistor M4 is disabled or turned off, and transistorM4 thereby electrically decouples the read word line RWL from node ND2.

In comparison with memory cell 300A of FIG. 3A, the drain terminal ofread transistor M2 of FIGS. 4A-4C is coupled with a reference voltagesupply. In some embodiments, the reference voltage supply has areference voltage VSS. In some embodiments, the reference voltage supplycorresponds to ground.

In comparison with memory cell 300A of FIG. 3A, the gate terminal oftransistor M3 of FIGS. 4A-4C is coupled with the read word line RWL.Transistor M3 of FIGS. 4A-4C is enabled or disabled in response to aread word line signal on the read word line RWL. Transistor M3 of FIGS.4A-4C is configured to electrically couple/decouple read transistor M2to/from the read bit line RBL in response to the read word line signalon the read word line RWL. For example, if the read word line signal islogically low, transistor M3 is enabled or turned on, and transistor M3thereby electrically couples the source of read transistor M2 to theread bit line RBL. For example, if the read word line signal islogically high, transistor M3 is disabled or turned off, and transistorM3 thereby electrically decouples the source of read transistor M2 fromthe read bit line RBL.

The operation of memory cell 400A is similar to the operation of memorycell 200A described above, and similar detailed description is thereforeomitted. For example, in comparison with the write operation of memorycell 200A of FIG. 2A and memory cell 300A of FIG. 3A, during the writeoperation of memory cell 400A, transistor M4 is enabled or disabled inresponse to the write bit line signal on the write bit line WBL,transistor M3 is enabled or disabled in response to the read word linesignal on the read word line RWL, and the operation of the otherportions of memory cell 400A are similar to the write operation ofmemory cell 200A described above, and similar detailed description istherefore omitted.

During a read operation of memory cell 400A, the voltage of the read bitline RBL is pre-charged to a logical high, and the read word line RWL islowered to a logical low causing transistor M3 to be enabled or turnedon. In some embodiments, if the read transistor M2 of FIGS. 4A-4C is ina low resistance state, then the read transistor M2 is turned on orconducting, and the voltage of the read bit line RBL is pulled towardsVSS by read transistor M2, and the voltage or current of the read bitline RBL is sensed by a sense amplifier (not shown), and the dataassociated with the read transistor M2 being in a low resistance state(e.g., “1” or “0”) is read out. In some embodiments, if the readtransistor M2 of FIGS. 4A-4C is in a high resistance state, then theread transistor M2 is turned off or not conducting, and the voltage ofthe read bit line RBL is not pulled towards VSS by read transistor M2,and the voltage or current of the read bit line RBL is sensed by a senseamplifier (not shown), and the data associated with the read transistorM2 being in a high resistance state (e.g., “1” or “0”) is read out. Inthis embodiment, the change in the voltage of the read bit line RBL isnegligible since the read transistor M2 is turned off. Afterwards, theread word line RWL is set to a logical high thereby causing transistorM3 to turn off.

Transistor M4 is shown as a PMOS transistor. In some embodiments,transistor M4 is an NMOS transistor.

In some embodiments, transistor M4 and at least write transistor M1,read transistor M2 or transistor M3, include channel regions that areformed of a same type of material. In some embodiments, transistor M4has a channel region that has a silicon body or bulk.

In some embodiments, by including write transistor M1, read transistorM2 (e.g., FeFET), transistor M3 and transistor M4, memory cell 400A issimilar to memory cell 200A. In some embodiments, since memory cell 400Ais similar to memory cell 200A, memory cell 400A has the benefitsdiscussed above with respect to memory cell 200A.

In some embodiments, memory cell 400A and memory cells 400B-400C (FIGS.4B-4C) have a 4T memory cell structure that is compatible with CMOSprocesses and is therefore scalable.

Other transistor terminals for each of transistors M1, M2, M3, M4, M1′,M2′, M3′ and M4′ of the present application are within the scope of thepresent disclosure. For example, reference to the drains and sources ofa same transistor in the present disclosure can be changed to a sourceand a drain of the same transistor.

Other configurations or quantities of transistors in memory cell 400Aare within the scope of the present disclosure.

FIG. 4B is a circuit diagram of a memory cell 400B, in accordance withsome embodiments.

Memory cell 400B is an embodiment of a memory cell in array of memorycells 102A of FIG. 1 expressed in a schematic diagram, and similardetailed description is therefore omitted.

Memory cell 400B is usable as one or more memory cells in array ofmemory cells 102A of FIG. 1 . Memory cell 400B includes write transistorM1′, read transistor M2, write word line WWL, read word line RWL, writebit line WBL, read bit line RBL, transistor M3 and transistor M4.

Memory cell 400B is a variation of memory cell 400A of FIG. 4A andmemory cell 200B of FIG. 2B, and similar detailed description istherefore omitted. For example, memory cell 400B combines featuressimilar to memory cell 400A of FIG. 4A and memory cell 200B of FIG. 2B.

In comparison with memory cell 400A of FIG. 4A, write transistor M1′ ofFIG. 2B replaces write transistor M1 of FIG. 4A, and similar detaileddescription is therefore omitted.

Write transistor M1′ is described in memory cell 200B of FIG. 2B, andsimilar detailed description is therefore omitted. Write transistor M1′is shown as a PMOS transistor. In some embodiments, write transistor M1′is an NMOS transistor. The operation of memory cell 400B is similar tothe operation of memory cell 400A described above, and similar detaileddescription is therefore omitted.

In some embodiments, by including write transistor M1′ with an oxidechannel region 210 and read transistor M2 (e.g., FeFET), transistor M3and transistor M4, memory cell 400B achieves benefits similar to thebenefits discussed above with respect to memory cell 400A and memorycell 200B.

Furthermore, since memory cell 400B is similar to memory cell 200A,memory cell 300B also has the benefits discussed above with respect tomemory cell 200A.

Other configurations, connections or quantities of transistors in memorycell 400B are within the scope of the present disclosure.

FIG. 4C is a circuit diagram of a memory cell 400C, in accordance withsome embodiments.

Memory cell 400C is an embodiment of a memory cell in array of memorycells 102A of FIG. 1 expressed in a schematic diagram, and similardetailed description is therefore omitted.

Memory cell 400C is usable as one or more memory cells in array ofmemory cells 102A of FIG. 1 . Memory cell 400C includes write transistorM1′, read transistor M2′, write word line WWL, read word line RWL, writebit line WBL, read bit line RBL, transistor M3′ and a transistor M4′.

Memory cell 400C is a variation of memory cell 400B of FIG. 4B, andsimilar detailed description is therefore omitted. In comparison withmemory cell 400B of FIG. 4B, read transistor M2′ replaces readtransistor M2 of FIG. 4B, transistor M3′ replaces transistor M3 of FIG.4B and transistor M4′ replaces transistor M4 of FIG. 4B, and similardetailed description is therefore omitted.

Read transistor M2′ is described in memory cell 200C of FIG. 2C, andsimilar detailed description is therefore omitted. Read transistor M2′is shown as a PMOS transistor. In some embodiments, read transistor M2′is an NMOS transistor.

Transistor M3′ is described in memory cell 300C of FIG. 3C, and similardetailed description is therefore omitted. Transistor M3′ is shown as aPMOS transistor. In some embodiments, transistor M3′ is an NMOStransistor.

Transistor M4′ is shown as a PMOS transistor. In some embodiments,transistor M4′ is an NMOS transistor. In some embodiments, transistorM4′ is similar to transistor M4 of FIGS. 4A-4B, and similar detaileddescription is therefore omitted. The operation of memory cell 400C issimilar to the operation of memory cell 400A (described above) or memorycell 400B, and similar detailed description is therefore omitted.

In comparison with transistor M4 of FIG. 4B, transistor M4′ includes anoxide channel region 240, and similar detailed description is thereforeomitted. In some embodiments, the oxide channel region 240 fortransistor M4′ includes an oxide semiconductor material including zincoxide, cadmium oxide, indium oxide, IGZO, SnO₂, TiO₂, or combinationsthereof, or the like.

In some embodiments, the oxide channel region 240 of transistor M4′includes the same oxide semiconductor material as the oxide channelregion 210, 220 or 230 of at least write transistor M1′, read transistorM2′ or transistor M3′. In some embodiments, the oxide channel region 240of transistor M4′ includes a different oxide semiconductor material asthe oxide channel region 210, 220 or 230 of at least write transistorM1′, read transistor M2′ or transistor M3′, respectively. Othertransistor types or oxide materials for transistor M4′ are within thescope of the present disclosure.

In some embodiments, one of read transistor M2′, transistor M3′ ortransistor M4′ includes an oxide channel region 220, 230 or 240, and theother of read transistor M2′, transistor M3′ or transistor M4 includes asilicon channel region having a silicon body or bulk similar to readtransistor M2, transistor M3 or transistor M4, respectively.

In some embodiments, by including write transistor M1′ with an oxidechannel region 210, read transistor M2′ with an oxide channel region 220and as an FeFET, transistor M3′ with an oxide channel region 230 andtransistor M4′ with an oxide channel region 240, memory cell 400Cachieves benefits similar to the benefits discussed above with respectto memory cell 400A and memory cell 200C. Furthermore, since memory cell400C is similar to memory cell 200A, memory cell 400C also has thebenefits discussed above with respect to memory cell 200A.

Other configurations, connections or quantities of transistors in memorycell 400C are within the scope of the present disclosure.

FIG. 5 is a cross-sectional view of an integrated circuit 500, inaccordance with some embodiments.

Integrated circuit 500 is an embodiment of read transistor M2 and M2′ ofFIGS. 2A-2C, 3A-3C and 4A-4C, and similar detailed description istherefore omitted. In some embodiments, integrated circuit 500 includesadditional elements not shown for ease of illustration.

Integrated circuit 500 is shown as a planar transistor; however, othertransistors are within the scope of the present disclosure. In someembodiments, integrated circuit 500 is a fin field effect transistor(FinFET), a nanosheet transistor, a nanowire transistor, or the like. Insome embodiments, integrated circuit 500 is an FeFET or the like, and ismanufactured as part of a back end of line (BEOL) process.

Integrated circuit 500 includes a substrate 502. In some embodiments,substrate 502 is a p-type substrate. In some embodiments, substrate 502is an n-type substrate. In some embodiments, substrate 502 includes anelemental semiconductor including silicon or germanium in crystal,polycrystalline, or an amorphous structure; a compound semiconductorincluding silicon carbide, gallium arsenic, gallium phosphide, indiumphosphide, indium arsenide, and indium antimonide; an alloysemiconductor including SiGe, GaAsP, AlInAs, AlGaAs, GaInAs, GaInP, andGaInAsP; any other suitable material; or combinations thereof. In someembodiments, the alloy semiconductor substrate has a gradient SiGefeature in which the Si and Ge composition change from one ratio at onelocation to another ratio at another location of the gradient SiGefeature. In some embodiments, the alloy SiGe is formed over a siliconsubstrate. In some embodiments, first substrate 502 is a strained SiGesubstrate. In some embodiments, the semiconductor substrate has asemiconductor on insulator structure, such as a silicon on insulator(SOI) structure. In some embodiments, the semiconductor substrateincludes a doped epi layer or a buried layer. In some embodiments, thecompound semiconductor substrate has a multilayer structure, or thesubstrate includes a multilayer compound semiconductor structure.

In some embodiments, integrated circuit 500 is a silicon transistor(e.g., has a silicon channel region (not labelled)), and substrate 502has a silicon body or bulk. In some embodiments, integrated circuit 500is an oxide transistor (e.g., has an oxide channel region 210, 220, 230or 240), and substrate 502 includes an oxide semiconductor materialincluding zinc oxide, cadmium oxide, indium oxide, IGZO, SnO₂, TiO₂, orcombinations thereof, or the like.

Integrated circuit 500 further includes a drain region 504 and a sourceregion 506 in substrate 502. In some embodiments, at least a portion ofsource region 506 or a portion of drain region 504 extends abovesubstrate 502. In some embodiments, the source region 506 and the drainregion 504 are embedded in substrate 502.

Drain region 504 is an embodiment of the drain terminal of readtransistor M2 and M2′ of FIGS. 2A-2C, 3A-3C and 4A-4C, and similardetailed description is therefore omitted. Source region 506 is anembodiment of the source terminal of read transistor M2 and M2′ of FIGS.2A-2C, 3A-3C and 4A-4C, and similar detailed description is thereforeomitted. In some embodiments, the drain region 504 and source region 506of FIG. 5 is referred to as an oxide definition (OD) region whichdefines the source or drain diffusion regions of integrated circuit 500or read transistor M2 and M2′ of FIGS. 2A-2C, 3A-3C and 4A-4C, andsimilar detailed description is therefore omitted.

In some embodiments, the drain region 504 and source region 506 of FIG.5 is referred to as an oxide definition (OD) region which defines thesource or drain diffusion regions of integrated circuit 500 or readtransistor M2 and M2′ of FIGS. 2A-2C, 3A-3C and 4A4C, and similardetailed description is therefore omitted.

In some embodiments, integrated circuit 500 is a P-type FeFETtransistor, therefore the substrate 502 is an N-type region, the drainregion 504 is a P-type active region having P-type dopants implanted insubstrate 502, and the source region 506 is a P-type active regionhaving P-type dopants implanted in substrate 502.

In some embodiments, integrated circuit 500 is an N-type FeFETtransistor, therefore the substrate 502 is a P-type region, the drainregion 504 is an N-type active region having N-type dopants implanted insubstrate 502, and the source region 506 is a an N-type active regionhaving N-type dopants implanted in substrate 502.

In some embodiments, N-type dopants include phosphorus, arsenic or othersuitable N-type dopants. In some embodiments, P-type dopants includeboron, aluminum or other suitable p-type dopants.

Integrated circuit 500 further includes an insulating layer 510 onsubstrate 502. In some embodiments, the insulating layer 510 is betweenthe drain region 504 and the source region 506. In some embodiments, theinsulating layer 510 is a gate dielectric layer. In some embodiments,the insulating layer includes an insulating material including SiO, SiO₂or combinations thereof, or the like. In some embodiments, insulatinglayer 510 includes a gate oxide or the like.

Integrated circuit 500 further includes a metal layer 512 over theinsulating layer 510. In some embodiments, the metal layer 512 includesCu, TiN, W or combinations thereof, or the like. In some embodiments,the metal layer 512 is a conductive layer including doped polysilicon.In some embodiments, integrated circuit 500 does not include metal layer512.

Integrated circuit 500 further includes a ferroelectric layer 520 overat least the conductive layer 512 or the insulating layer 510. In someembodiments, where integrated circuit 500 does not include metal layer512, ferroelectric layer 520 is on the insulating layer 510.Ferroelectric layer 520 is an embodiment of ferroelectric region 202 ofFIGS. 2A-2C, 3A-3C and 4A4C, and similar detailed description istherefore omitted.

In some embodiments, ferroelectric layer 520 includes a ferroelectricmaterial. In some embodiments, a ferroelectric material includes HfO₂,HfZrO, HfO, perovskite, SBT, PZT or combinations thereof, or the like.

Ferroelectric layer 520 has polarization states P1 or P2 that correspondto polarization states P+ or P− in FIG. 2A, and similar detaileddescription is therefore omitted. Polarization state P1 points in afirst direction Y. Polarization state P2 points in a second direction(e.g., negative Y) opposite of the first direction Y.

FIG. 5 shows both polarization states P1 and P2. However, in someembodiments, due to the non-volatility of the ferroelectric layer 520,once the polarization state P1 or P2 of integrated circuit 500 is setbased on the gate voltage VG, integrated circuit 500 includes one of thepolarization states P1 or P2.

The ferroelectric layer 520 creates a capacitance in integrated circuit500. Furthermore, the MOS transistor of integrated circuit 500 also hasa capacitance. In some embodiments, the capacitance of the ferroelectriclayer 520 and the capacitance of the MOS transistor are matched tooperate integrated circuit 500 in a non-volatile mode. In someembodiments, the capacitance of the ferroelectric layer 520 is adjustedbased on a thickness T1 of the ferroelectric layer 520. In someembodiments, by changing thickness T1, integrated circuit 500 canoperate in a non-volatile mode or a volatile mode.

In some embodiments, the thickness T1 of the ferroelectric layer 520ranges from about 3 nanometers (nm) to about 50 nm. In some embodiments,as the thickness T1 increases, the ability of the ferroelectric layer520 to preserve the hysteresis and bi-stable polarization states (e.g.,P1 or P2) is increased and the leakage current of integrated circuit 500decreases. In some embodiments, as the thickness T1 decreases, theability of the ferroelectric layer 520 to preserve the hysteresis andbi-stable polarization states (e.g., P1 or P2) is reduced and theleakage current of integrated circuit 500 increases. In someembodiments, integrated circuit 500 does not include the insulatinglayer 510 and metal layer 512, and the ferroelectric layer 520 isdirectly on substrate 502. In some embodiments, integrated circuit 500does not include the insulating layer 510, and the metal layer 512 isdirectly on substrate 502.

Integrated circuit 500 further includes a gate structure 530 over theferroelectric layer 520. The gate structure 530 includes a conductivematerial such as a metal or doped polysilicon (also referred to hereinas “POLY”).

In some embodiments, integrated circuit 500 is an embodiment of writetransistor M1 and M1′ of FIGS. 2A-2C, 3A-3C and 4A-4C. In theseembodiments, integrated circuit 500 does not include the ferroelectriclayer 520.

By being included in memory cell array 100 and memory circuit 200A-200C,300A-300C and 400A-400C discussed above with respect to FIGS. 1, 2A-2C,3A-3C and 4A-4C, integrated circuit 500 operates to achieve the benefitsdiscussed above with respect to memory cell array 100 and memory circuit200A-200C, 300A-300C and 400A-400C.

FIG. 6 is a functional flow chart of a method 600 of manufacturing anintegrated circuit (IC), in accordance with some embodiments. It isunderstood that additional operations may be performed before, during,and/or after the method 600 depicted in FIG. 6 , and that some otherprocesses may only be briefly described herein. In some embodiments,other order of operations of method 600 is within the scope of thepresent disclosure. Method 600 includes exemplary operations, but theoperations are not necessarily performed in the order shown. Operationsmay be added, replaced, changed order, and/or eliminated as appropriate,in accordance with the spirit and scope of disclosed embodiments. Insome embodiments, one or more of the operations of method 600 is notperformed.

In some embodiments, the method 600 is usable to manufacture orfabricate at least memory cell array 100 (FIG. 1 ), memory cell200A-200C, 300A-300C or 400A-400C (FIG. 2A-2C, 3A-3C or 4A-4C) orintegrated circuit 500 (FIG. 5 ).

In operation 602 of method 600, the drain region 504 of a transistor isfabricated in substrate 502. In some embodiments, the drain region ofmethod 600 includes at least the drain of read transistor M2 or M2′. Insome embodiments, the transistor of method 600 includes at least readtransistor M2 or M2′. In some embodiments, the drain region isfabricated in a first well within the substrate, and the first well hasa dopant opposite of the dopant of the drain region.

In some embodiments, the transistor of method 600 includes at leasttransistor M1, M1′, M3, M3′, M4 or M4′. In some embodiments, the drainregion of method 600 includes at least the drain of transistor M1, M1′,M3, M3′, M4 or M4′.

In operation 604 of method 600, the source region 504 of the transistoris fabricated in substrate 502. In some embodiments, the source regionof method 600 includes at least the source of read transistor M2 or M2′.In some embodiments, the transistor of method 600 includes at least readtransistor M2 or M2′. In some embodiments, the source region isfabricated in the first well. In some embodiments, the source region ofmethod 600 includes at least the source of transistor M1, M1′, M3, M3′,M4 or M4′.

In some embodiments, at least operation 602 or 604 includes theformation of source/drain features that are formed in the substrate. Insome embodiments, the formation of the source/drain features includes, aportion of the substrate is removed to form recesses, and a fillingprocess is then performed by filling the recesses in the substrate. Insome embodiments, the recesses are etched, for example, a wet etching ora dry etching, after removal of a pad oxide layer or a sacrificial oxidelayer. In some embodiments, the etch process is performed to remove atop surface portion of the active region. In some embodiments, thefilling process is performed by an epitaxy or epitaxial (epi) process.In some embodiments, the recesses are filled using a growth processwhich is concurrent with an etch process where a growth rate of thegrowth process is greater than an etch rate of the etch process. In someembodiments, the recesses are filled using a combination of growthprocess and etch process. For example, a layer of material is grown inthe recess and then the grown material is subjected to an etch processto remove a portion of the material. Then a subsequent growth process isperformed on the etched material until a desired thickness of thematerial in the recess is achieved. In some embodiments, the growthprocess continues until a top surface of the material is above the topsurface of the substrate. In some embodiments, the growth process iscontinued until the top surface of the material is co-planar with thetop surface of the substrate. In some embodiments, a portion ofsubstrate 502 is removed by an isotropic or an anisotropic etch process.The etch process selectively etches substrate 502 without etching gatestructure 530. In some embodiments, the etch process is performed usinga reactive ion etch (RIE), wet etching, or other suitable techniques. Insome embodiments, a semiconductor material is deposited in the recessesto form the source/drain features. In some embodiments, an epi processis performed to deposit the semiconductor material in the recesses. Insome embodiments, the epi process includes a selective epitaxy growth(SEG) process, CVD process, molecular beam epitaxy (MBE), other suitableprocesses, and/or combination thereof. The epi process uses gaseousand/or liquid precursors, which interacts with a composition of thesubstrate. In some embodiments, the source/drain features includeepitaxially grown silicon (epi Si), silicon carbide, or silicongermanium. Source/drain features of the IC device associated with gatestructure 530 are in-situ doped or undoped during the epi process insome instances. When source/drain features are undoped during the epiprocess, source/drain features are doped during a subsequent process insome instances. The subsequent doping process is achieved by an ionimplantation, plasma immersion ion implantation, gas and/or solid sourcediffusion, other suitable processes, and/or combination thereof. In someembodiments, source/drain features are further exposed to annealingprocesses after forming source/drain features and/or after thesubsequent doping process.

In some embodiments, source/drain features have n-type dopants thatinclude phosphorus, arsenic or other suitable n-type dopants. In someembodiments, the n-type dopant concentration ranges from about 1×10¹²atoms/cm2 to about 1×10¹⁴ atoms/cm2.

In some embodiments, source/drain features have p-type dopants thatinclude boron, aluminum or other suitable p-type dopants. In someembodiments, the p-type dopant concentration ranges from about 1×10¹²atoms/cm2 to about 1×10¹⁴ atoms/cm2.

In operation 606 of method 600, an insulating layer 510 is fabricated onthe substrate 502. In some embodiments, at least fabricating theinsulating layer 510 of operation 610 includes performing one or moredeposition processes to form one or more dielectric material layers. Insome embodiments, a deposition process includes a chemical vapordeposition (CVD), a plasma enhanced CVD (PECVD), an atomic layerdeposition (ALD), or other process suitable for depositing one or morematerial layers.

In operation 608 of method 600, a conductive layer is deposited on theinsulating layer 510. In some embodiments, the conductive layer ofmethod 600 is metal layer 512. In some embodiments, the conductive layerof operation 608 is formed using a combination of photolithography andmaterial removal processes to form openings in an insulating layer (notshown) over the substrate. In some embodiments, the photolithographyprocess includes patterning a photoresist, such as a positivephotoresist or a negative photoresist. In some embodiments, thephotolithography process includes forming a hard mask, an antireflectivestructure, or another suitable photolithography structure. In someembodiments, the material removal process includes a wet etchingprocess, a dry etching process, an RIE process, laser drilling oranother suitable etching process. The openings are then filled withconductive material, e.g., copper, aluminum, titanium, nickel, tungsten,or other suitable conductive material. In some embodiments, the openingsare filled using CVD, PVD, sputtering, ALD or other suitable formationprocess.

In operation 610 of method 600, a ferroelectric layer 520 is formed onat least the insulating layer 510 or the conductive layer (metal layer512). In some embodiments, at least operation 606 or 608 is notperformed. In some embodiments, operations 606 and 608 are notperformed, and the ferroelectric layer 520 is formed directly onsubstrate 502. In some embodiments, operation 606 is not performed andthe conductive layer (e.g., metal layer 512) is deposited on substrate502. In some embodiments, operation 608 is not performed and theferroelectric layer 520 is deposited on insulating layer 510.

In operation 612 of method 600, a gate region 530 of the transistor isfabricated. In some embodiments, fabricating the gate region includesperforming one or more deposition processes to form one or moreconductive material layers. In some embodiments, fabricating the gateregions includes forming gate electrodes. In some embodiments, gateregions are formed using a doped or non-doped polycrystalline silicon(or polysilicon). In some embodiments, the gate regions include a metal,such as Al, Cu, W, Ti, Ta, TiN, TaN, NiSi, CoSi, other suitableconductive materials, or combinations thereof.

FIG. 7 is a flowchart of a method 700 of operating a circuit, inaccordance with some embodiments. In some embodiments, FIG. 7 is aflowchart of method 700 of operating a memory circuit, such as memorycell array 100 of FIG. 1 or memory cell 200A-200C, 300A-300C or400A-400C (FIG. 2A-2C, 3A-3C or 4A-4C) or integrated circuit 500 (FIG. 5).

It is understood that additional operations may be performed before,during, and/or after the method 700 depicted in FIG. 7 , and that someother processes may only be briefly described herein. In someembodiments, other order of operations of method 700 is within the scopeof the present disclosure. Method 700 includes exemplary operations, butthe operations are not necessarily performed in the order shown.Operations may be added, replaced, changed order, and/or eliminated asappropriate, in accordance with the spirit and scope of disclosedembodiments. In some embodiments, one or more of the operations ofmethod 700 is not performed.

In operation 702 of method 700, a write operation of a memory cell isperformed. In some embodiments, the memory cell of method 700 includesmemory cell 200A-200C, 300A-300C or 400A-400C. In some embodiments, thememory cell of method 700 includes at least a memory cell of memory cellarray 100. In some embodiments, operation 702 includes at leastoperation 704, 706, 708 or 710.

In operation 704 of method 700, a write bit line signal is set on awrite bit line WBL. In some embodiments, the write bit line signal ofmethod 700 includes a write bit line signal of write bit line WBL. Insome embodiments, the write bit line signal corresponds to a stored datavalue in the memory cell.

In operation 706 of method 700, a write transistor is turned on inresponse to a write word line signal thereby electrically coupling thewrite bit line WBL to a gate of a read transistor. In some embodiments,the write transistor of method 700 includes at least write transistor M1or M1′. In some embodiments, the read transistor of method 700 includesat least read transistor M2 or M2′. In some embodiments, the gate ofread transistor of method 700 includes at least the gate terminal ofread transistor M2 or M2′. In some embodiments, the write word linesignal of method 700 includes a write word line signal of write wordline WWL. In some embodiments, the read transistor of method 700includes integrated circuit 500. In some embodiments, the writetransistor of method 700 includes integrated circuit 500.

In operation 708 of method 700, the stored data value of the memory cellis set by adjusting a polarization state of the read transistor therebyturning on or off the read transistor.

In some embodiments, the polarization state of the read transistor ofmethod 700 includes the polarization state P+ or P− of at least readtransistor M2 or M2′. In some embodiments, the polarization state of theread transistor of method 700 includes the polarization state P1 or P2of integrated circuit 500. In some embodiments, the polarization statecorresponds to the stored data value of the memory cell.

In operation 710 of method 700, the write transistor is turned off inresponse to the write word line signal thereby electrically decouplingthe write bit line and the gate of the read transistor from each other.In some embodiments, operation 710 further includes holding the storeddata value in the memory cell.

In operation 712 of method 700, a read operation of the memory cell isperformed. In some embodiments, operation 712 includes at leastoperation 714, 716, 718 or 720.

In operation 714 of method 700, a voltage of a read bit line RBL ispre-discharged to a first voltage (VSS) or the voltage of the read bitline RBL is pre-charged to a second voltage (VDD) different from thefirst voltage. In some embodiments, the first voltage of method 700includes reference voltage VSS. In some embodiments, the second voltageof method 700 includes supply voltage VDD.

In operation 716 of method 700, a voltage of a read word line RWL isadjusted from a third voltage to a fourth voltage. In some embodiments,the voltage of the read word line RWL is the read word line signal. Insome embodiments, the third voltage of method 700 includes a voltage ofa logically high signal. In some embodiments, the third voltage ofmethod 700 includes a supply voltage VDD. In some embodiments, thefourth voltage of method 700 includes a voltage of a logically lowsignal. In some embodiments, the fourth voltage of method 700 includes areference voltage VSS.

In operation 718 of method 700, the voltage of the read bit line issensed in response to adjusting the voltage of the read word line fromthe third voltage to the fourth voltage thereby outputting the storeddata value in the memory cell. In some embodiments, rather than sensingthe voltage of the read word line, operation 718 includes sensing thecurrent of the read bit line in response to adjusting the voltage of theread word line from the third voltage to the fourth voltage therebyoutputting the stored data value in the memory cell.

In some embodiments, the stored data value of the memory cell has afirst logical value corresponding to a first resistance state of theread transistor, or a second logical value corresponding to a secondresistance state of the read transistor. In some embodiments, the secondlogical value is opposite of the first logical value. In someembodiments, the second resistance state is opposite of the firstresistance state. In some embodiments, first logical value is one oflogical 1 or logical 0, and the second logical value is the other oflogical 0 or logical 1. In some embodiments, the first resistance stateis one of the low resistance state or the high resistance state and thesecond resistance state is the other of the high resistance state or thelow resistance state.

In some embodiments, adjusting the voltage of the read word line RWLfrom the third voltage to the fourth voltage of operation 718 comprisesturning on a first transistor in response to a first control signal orthe voltage of the read word line being the fourth voltage therebyelectrically coupling the read bit line to a source of the readtransistor. In some embodiments, the first transistor of method 700includes transistor M3 or M3′. In some embodiments, the first controlsignal of method 700 includes control signal CS. In some embodiments,the source of the read transistor of method 700 includes the sourceterminal of read transistor M2 or M2′.

In operation 720 of method 700, the voltage of the read word line isadjusted from the fourth voltage to the third voltage. In someembodiments, adjusting the voltage of the read word line from the fourthvoltage to the third voltage of operation 720 comprises turning off thefirst transistor in response to the first control signal or the voltageof the read word line being the third voltage thereby electricallydecoupling the read bit line and the source of the read transistor fromeach other.

By operating method 700, the memory circuit operates to achieve thebenefits discussed above with respect to memory cell array 100 of FIG. 1or memory cell 200A-200C, 300A-300C or 400A-400C (FIG. 2A-2C, 3A-3C or4A-4C) or integrated circuit 500 (FIG. 5 ).

While method 700 was described above with reference to a single memorycell of memory cell array 100, it is understood that method 700 appliesto each row and each column of memory cell array 100, in someembodiments.

Furthermore, various PMOS or NMOS transistors shown in FIG. 2A-2C, 3A-3Cor 4A-4C are of a particular dopant type (e.g., N-type or P-type) arefor illustration purposes. Embodiments of the disclosure are not limitedto a particular transistor type, and one or more of the PMOS or NMOStransistors shown in FIG. 2A-2C, 3A-3C or 4A-4C can be substituted witha corresponding transistor of a different transistor/dopant type.Similarly, the low or high logical value of various signals used in theabove description is also for illustration. Embodiments of thedisclosure are not limited to a particular logical value when a signalis activated and/or deactivated. Selecting different logical values iswithin the scope of various embodiments. Selecting different numbers oftransistors in FIG. 2A-2C, 3A-3C or 4A-4C is within the scope of variousembodiments.

It will be readily seen by one of ordinary skill in the art that one ormore of the disclosed embodiments fulfill one or more of the advantagesset forth above. After reading the foregoing specification, one ofordinary skill will be able to affect various changes, substitutions ofequivalents and various other embodiments as broadly disclosed herein.It is therefore intended that the protection granted hereon be limitedonly by the definition contained in the appended claims and equivalentsthereof.

One aspect of this description relates to a memory cell. The memory cellincludes a write bit line, a write transistor and a read transistor. Thewrite transistor is coupled between the write bit line and a first node.The read transistor is coupled to the write transistor by the firstnode. The read transistor includes a ferroelectric layer. The writetransistor is configured to set a stored data value of the memory cellby a write bit line signal that adjusts a polarization state of the readtransistor. In some embodiments, the polarization state corresponds tothe stored data value.

Another aspect of this description relates to a memory cell. The memorycell includes a write bit line, a write word line, a write transistor ofa first type and a read transistor of the first type. In someembodiments, the write transistor is coupled to the write bit line, thewrite word line and a first node. In some embodiments, the writetransistor is configured to be enabled or disabled in response to awrite word line signal. In some embodiments, the read transistorincludes a first gate terminal coupled to the write transistor by thefirst node, and a ferroelectric layer having a polarization state thatcorresponds to a stored data value in the memory cell. In someembodiments, the write transistor is configured to set the stored datavalue in the memory cell by the write word line signal that adjusts thepolarization state of the ferroelectric layer.

Still another aspect of this description relates to a method ofoperating a memory cell. The method includes performing a writeoperation of the memory cell. In some embodiments, the performing thewrite operation of the memory cell includes setting a write bit linesignal on a write bit line, the write bit line signal corresponding to astored data value in the memory cell. In some embodiments, theperforming the write operation of the memory cell further includesturning on a write transistor in response to a write word line signalthereby electrically coupling the write bit line to a gate of a readtransistor. In some embodiments, the performing the write operation ofthe memory cell further includes setting the stored data value of thememory cell by adjusting a polarization state of the read transistorthereby turning on or off the read transistor, the polarization statecorresponding to the stored data value of the memory cell. In someembodiments, the performing the write operation of the memory cellfurther includes turning off the write transistor in response to thewrite word line signal thereby electrically decoupling the write bitline and the gate of the read transistor from each other.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A memory cell, comprising: a write bit line; awrite transistor coupled between the write bit line and a first node; aread transistor coupled to the write transistor by the first node,wherein the read transistor includes a ferroelectric layer, a drainterminal of the read transistor coupled to a second node, and a sourceterminal of the read transistor coupled to a third node; a firsttransistor coupled to the read transistor, the first transistorcomprising: a drain terminal of the first transistor coupled to thesource terminal of the read transistor by the third node; and a sourceterminal of the first transistor coupled to a read bit line; and asecond transistor coupled to the read transistor and the writetransistor by the first node, the second transistor comprising: a drainterminal of the second transistor coupled to a read word line; a sourceterminal of the second transistor coupled to a fourth node; and a gateterminal of the second transistor coupled to a source terminal of thewrite transistor and a gate terminal of the read transistor by the firstnode; wherein the write transistor is configured to set a stored datavalue of the memory cell by a write bit line signal that adjusts apolarization state of the read transistor, the polarization statecorresponding to the stored data value.
 2. The memory cell of claim 1,wherein the write transistor comprises: a drain terminal of the writetransistor coupled to the write bit line; the source terminal of thewrite transistor coupled to the first node and the read transistor; anda gate terminal of the write transistor coupled to a write word line. 3.The memory cell of claim 2, wherein the read transistor furtherincludes: a gate terminal of the read transistor on the ferroelectriclayer and being coupled to the source terminal of the write transistorby the first node.
 4. The memory cell of claim 1, wherein the drainterminal of the read transistor is coupled to a reference voltage supplyby the second node; and the first transistor further comprises: a gateterminal of the first transistor coupled to the read word line.
 5. Amemory cell, comprising: a write bit line; a write word line; a writetransistor of a first type, coupled to the write bit line, the writeword line and a first node, the write transistor configured to beenabled or disabled in response to a write word line signal; and a readtransistor of the first type, the read transistor comprising: a firstgate terminal of the read transistor coupled to the write transistor bythe first node; and a ferroelectric layer having a polarization statethat corresponds to a stored data value in the memory cell; a firsttransistor coupled to the read transistor, the first transistorcomprising: a drain terminal of the first transistor coupled to a sourceterminal of the read transistor; a source terminal of the firsttransistor coupled to a read bit line; and a gate terminal of the firsttransistor coupled to a read word line; and a second transistor coupledto the read transistor and the write transistor by the first node, thesecond transistor comprising: a drain terminal of the second transistorcoupled to the read word line; a source terminal of the secondtransistor coupled to a second node; and a gate terminal of the secondtransistor coupled to a source terminal of the write transistor and thefirst gate terminal of the read transistor by the first node; wherein adrain terminal of the read transistor is coupled to a reference voltagesupply; wherein the write transistor is configured to set the storeddata value in the memory cell by a write bit line signal that adjuststhe polarization state of the ferroelectric layer.
 6. The memory cell ofclaim 5, wherein the write transistor includes an oxide channel region;and the read transistor includes a silicon channel region.
 7. The memorycell of claim 5, wherein the write transistor includes an oxide channelregion; and the read transistor includes another oxide channel region.8. The memory cell of claim 5, wherein the read transistor furthercomprises: a gate insulating layer over a channel region of the readtransistor; a gate layer on the ferroelectric layer; wherein theferroelectric layer is between the gate insulating layer and the gatelayer.
 9. The memory cell of claim 5, wherein the ferroelectric layerincludes a ferroelectric material including HfO₂, HfZrO, HfO orcombinations thereof.
 10. A method of operating a memory cell, themethod comprising: performing a write operation of the memory cell, theperforming the write operation of the memory cell comprising: setting awrite bit line signal on a write bit line, the write bit line signalcorresponding to a stored data value in the memory cell; turning on awrite transistor in response to a write word line signal therebyelectrically coupling the write bit line to a gate of a read transistor;setting the stored data value of the memory cell by adjusting apolarization state of the read transistor thereby turning on or off theread transistor, the polarization state corresponding to the stored datavalue of the memory cell; and turning off the write transistor inresponse to the write word line signal thereby electrically decouplingthe write bit line and the gate of the read transistor from each other;and performing a read operation of the memory cell, the performing theread operation of the memory cell comprising: pre-discharging a voltageof a read bit line to a first voltage or pre-charging the voltage of theread bit line to a second voltage different from the first voltage;adjusting a voltage of a read word line from a third voltage to a fourthvoltage; sensing the voltage of the read bit line in response toadjusting the voltage of the read word line from the third voltage tothe fourth voltage thereby outputting the stored data value in thememory cell; and adjusting the voltage of the read word line from thefourth voltage to the third voltage.
 11. The method of claim 10, whereinadjusting the voltage of the read word line from the third voltage tothe fourth voltage comprises: turning on a first transistor in responseto a first control signal or the voltage of the read word line being thefourth voltage thereby electrically coupling the read bit line to asource of the read transistor.
 12. The method of claim 10, whereinadjusting the voltage of the read word line from the fourth voltage tothe third voltage comprises: turning off a first transistor in responseto a first control signal or the voltage of the read word line being thethird voltage thereby electrically decoupling the read bit line and asource of the read transistor from each other.
 13. The method of claim10, wherein the stored data value of the memory cell has a first logicalvalue corresponding to a first resistance state of the read transistor,or a second logical value corresponding to a second resistance state ofthe read transistor, the second logical value being opposite of thefirst logical value, the second resistance state being opposite of thefirst resistance state.
 14. The memory cell of claim 1, wherein thewrite transistor includes an oxide channel region; and the readtransistor includes a silicon channel region.
 15. The memory cell ofclaim 1, wherein the write transistor includes an oxide channel region;and the read transistor includes another oxide channel region.
 16. Thememory cell of claim 1, wherein the read transistor further includes: achannel region of the read transistor; a gate insulating layer over thechannel region of the read transistor; a gate layer on the ferroelectriclayer; wherein the ferroelectric layer is between the gate insulatinglayer and the gate layer.
 17. The memory cell of claim 16, wherein theread transistor further includes: a metal layer over the gate insulatinglayer, wherein the metal layer is between the gate insulating layer andthe ferroelectric layer.
 18. The memory cell of claim 1, wherein theferroelectric layer includes a ferroelectric material including HfO₂,HfZrO, HfO or combinations thereof.
 19. The memory cell of claim 1,wherein the first transistor further comprises: a gate terminal of thefirst transistor coupled to the drain terminal of the second transistorand the read word line.
 20. The memory cell of claim 1, wherein thesource terminal of the second transistor is electrically floating.